An indium-containing oxide is transparent and conducts electricity, and thus has been widely used in the industry. Due to a higher conductivity or other advantages, a composite indium oxide film containing indium and other metals or an indium oxide film doped with other elements such as fluorine are commonly used rather than an indium oxide film containing indium only. By way of example, an indium tin oxide (ITO) has been used as an electrode of a liquid crystal display (LCD) for a long time. In recent years, researches for using an oxide (In—Ga—Zn—O, IGZO) containing indium, gallium, and zinc in a transparent thin film transistor have been actively carried out. In addition to Sn, Ga, and Zn, other metals such as Al and Mg, and so on also may be used in a composite oxide film containing indium. Most of ITO films used in the current industry have been prepared by a sputtering method. As described in International Patent Application Publication No. WO2010/024279 (Korean Patent Publication No. 10-2011-0028393), an IGZO film is also generally prepared by a sputtering method.
Chemical vapor deposition (CVD) or atomic layer deposition in which source gases are alternately brought into contact with a substrate has an advantage of being able to form a film having a uniform thickness on an uneven surface.
Elam et al. reported a method for forming In2O3 and ITO films by atomic layer deposition using cyclopentadienyl indium (CpIn) which is a solid at room temperature [J. W. Elam et al., “Atomic Layer Deposition of In2O3 Using Cyclopentadienyl Indium: A New Synthetic Route to Transparent Conducting Oxide Films”, Chemistry of Materials, Volume 18, p 3571 (2006); J. W. Elam et al., “Atomic Layer Deposition of Indium Tin Oxide Thin Films Using Nonhalogenated Precursors” Journal of Physical Chemistry C, volume 112, p 1938 (2008)]. It is very difficult to vaporize a solid compound and supply it to a large-area substrate at a uniform concentration, and, thus, it is difficult to industrially apply a method for forming In2O3 and ITO films on a large-area substrate using CpIn as an indium source.
There have been known methods for forming an indium oxide film or an indium-containing oxide film by chemical vapor deposition or atomic layer deposition using other indium compounds instead of CpIn as a source material. Ritala et al. reported a method for forming an indium oxide film or an ITO film by atomic layer deposition using InCl3 and SnCl4 [M. Ritala et al., “Enhanced Growth Rate in Atomic Layer Epitaxy of Indium Oxide and Indium-Tin Oxide Thin Films”, Electrochemical and Solid-State Letters, volume 1, p 156 (1998)]. InCl3 is a solid at room temperature, and in order to supply InCl3 in a gaseous state, a source supply unit needs to be heated at a high temperature of 285° C. Ritala et al. also reported a method for forming a conductive indium oxide film, ITO, and an indium oxide film doped with fluorine using In(hfac)3, In(thd)3, and In(acac)3 which are solids at room temperature (hfac=hexafluoropentadionate; thd=2,2,6,6-tetramethyl-3,5-heptanedionate; acac=2,4-pentanedionate) [M. Ritala et al., “ALE Growth of Transparent Conductors”, Material Research Society Symposium Proceedings, volume 426, p 513 (1996)]. Nielsen et al. reported a method for forming an indium oxide film by atomic layer deposition using In(acac)3 [O. Nielsen et al., “Thin films of In2O3 by atomic layer deposition using In(acac)3”, Thin Solid Films, volume 517, p 6320 (2009)]. Ott et al. reported a method for forming an indium oxide film using In(CH3)3 which is a solid at room temperature [A. W. Ott et al., “Surface chemistry of In2O3 deposition using In(CH3)3 and H2O in a binary reaction sequence”, Applied Surface Science, volume 112, p 205 (1997)]. Jin Ho Park et al. reported a method for forming an indium oxide film using [(CH3)2In(acac)]2 which is a solid at room temperature [J.-H. Park et al., “The X-ray single crystal structure of [Me2In(acac)]2 and its use as a single-source precursor for the deposition of indium oxide thin films”, Journal of Materials Chemistry, volume 11, p 2346 (2001)]. Gaskell and Sheel also reported a method for forming an indium oxide film doped with fluorine using [(CH3)2In(acac)]2 [D. W. Sheel and J. M. Gaskell, “Deposition of fluorine doped indium oxide by atmospheric pressure chemical vapour deposition”, Thin Solid Films, volume 520, p 1242 (2011)]. Barry et al. reported a method for forming an indium oxide film by chemical vapor deposition using In[(NiPr)2CN(CH3)2]3 which is a solid at room temperature, as a source material [S. T. Barry et al., “Chemical vapour deposition of In2O3 thin films from a tris-guanidinate indium precursor”, Dalton Transactions, volume 40, p 9425 (2011)].
So far, all of the indium sources used for forming indium oxide films or indium-containing oxide films are solids at room temperature. There has not been known a method for forming an indium oxide film or an indium-containing oxide film by chemical vapor deposition or atomic layer deposition using an indium compound which is a liquid at room temperature. Further, there has not been known an example of forming, via chemical vapor deposition or atomic layer deposition, indium oxide film or indium-containing oxide film having a high conductivity equivalent to that of an indium-containing oxide film formed by a sputtering method so as to be used as a transparent electrode.
A thin film transistor using IGZO is higher in speed than a thin film transistor using a non-crystalline silicon, and, thus, researches for applying it to a large-area LCD panel such as a TV, and so on have been actively carried out. It is necessary to form IGZO by chemical vapor deposition or atomic layer deposition in order to control a composition of an IGZO oxide film, but it is very difficult to form an indium oxide film or indium-containing oxide film on a display glass substrate even larger than 1 meter in width and length using a source material which is a solid at room temperature.
In order to form an IGZO film on a large-area substrate, especially a large-area display substrate which can be applied to a TV, and so on, it is necessary to form an indium oxide film or indium-containing oxide film by chemical vapor deposition or atomic layer deposition using a liquid indium compound. In particular, in the case of using a glass substrate, it is necessary to form an indium oxide film or indium-containing oxide film by chemical vapor deposition or atomic layer deposition using a liquid indium compound at a temperature of 200° C. or less.